The present invention pertains to automatic gain controls, and more particularly to automatic gain control for a receiver, and to allocation of a channel.
A variety of devices are known that include transceivers used in communications with other compatible devices. Examples of such devices include wireless communication devices such as radio telephones, which may be cordless or cellular, two-way radios, base stations, pagers, and wire line or cable communication devices such as modems, data terminals, or the like. These devices typically include a circuitry to control the transmit and receive path gain such that receive signals are output at a somewhat uniform signal level.
Wireless communication systems are particularly difficult to provide power control as the environment is by its nature very dynamic. The distance between a mobile devices, or a mobile device and a base station, is subject to constant change. Additionally, the transmission path may change as obstructions move into the transmission path between the mobile device an another device. For example, buildings, hills, and other obstructions move in and out of the transmission path of a cellular radiotelephone as it moves. These obstructions will negatively impact on the level of the signal received by the bast station and the mobile device during a communication exchange.
Accordingly, systems such as the Global System for Mobile Communications (GSM, require radio frequency (RF) power control. The objective of such power control is to achieve the minimum amount of power needed for adequate wireless communication quality. By limiting the level of signals communicated, the average amount of RF spectral energy detected by surrounding mobiles and base stations is reduced. This has the effect of reducing interference, as the level of interference on an RF channel is the sum of the contributions from all of RF sources.
The purpose of the RF power control is therefor to reduce the amount of channel interference present on each channel. This increases the link reliability and the capacity of the channels.
For example, the GSM standard for circuit switched voice telephony specifies that the range over which the base station subsystem (BSS) RF power is to be controlled extends from the station""s maximum to 30 dB below the maximum. The standard specifies similar requirements for the mobile station, depending upon the power output class of the mobile.
However, for General Packet Radio Service (GPRS), power control is significantly more difficult to achieve. This is due to the variant length of data packets and variations in the time period between transmission of data packets between the base station and the mobile station in GPRS mode.
The method of control specified for transmissions from the base station to the mobile station in the GSM GPRS example requires that the BTS must transmit the four bursts which comprise a single data block at the same power level. However, this standard also permits control of the base transceiver station (BTS) on a block-by-block basis based on Channel Quality Reports.
The extent of power control on the transmission of data blocks under this exemplary standard can extend from the value of the output power transmitted by the base transceiver station on the broadcast control channel (BCCH) to a level 30 dB below the BCCH carrier. Additionally, a GPRS mobile may be required to receive down link data blocks on more than one time slot. For example, the amplitude of two four-burst intervals which comprise a block of data may differ.
These factors combine to present difficulties in implementing an effective AGC function for mobile stations. One proposal that has been made is to provide data in one transmission that indicates the attenuation amount, relative to the RF power level of the BCCH carrier, at which the next base transceiver station data block will be transmitted.
However, their are problems associated with accepting this type of information. For example, it is difficult to achieve initial acquisition of automatic gain control (AGC). There are problems associated with processing actions to set the AGC level in the absence of a decodable signal, such as intermittent decode errors distributed over a down link transfer. Additional problems will occur when attempting to decode data in more that one time slot. Most problematic however, is accommodating dynamic time slot allocation for mobile transmissions, where the mobile is required to monitor all time slots, some of which may be addressed to other mobiles, in order to receive an assignment of which up link time slot on which it is to transmit.
Accordingly, there is need for an improved method of providing automatic gain control in a receiver for a dynamic system.